Optimize BaseEventLoop._run_once()
Optimize BaseEventLoop._run_once()

Logger.log() is "slow", logger.isEnabledFor() is faster and the logger is
disabled in most cases. A microbenchmark executing 100,000 dummy tasks is 22%
faster with this change.

See the CPython issue: http://bugs.python.org/issue20275

leetreveil/tulip,leetreveil/tulip,overcastcloud/trollius,overcastcloud/trollius,overcastcloud/trollius,leetreveil/tulip